This invention relates to the synthesis of beryl single crystals, and more particularly to synthesis of beryl single crystals from a raw material having a composition substantially similar to that of natural beryl and including at least one material selected from molybdates, vanadates and tungstates.
The composition of natural beryl crystal is 3BeO.Al.sub.2 O.sub.3.6SiO.sub.2 and has a hexagonal crystalline structure. Beryl crystal is an incongruent melting material temperature of about 1410.degree. C. The hydrothermal process and the flux process are the main conventional synthetic processes for synthesizing beryl crystal. Specifically, the flux process has been in practical use and green emerald crystals have appeared on the market wherein chromium element has been doped into the flux.
The production costs in the flux process are extremely high for the following reasons.
1. It is necessary to utilize a platinum crucible.
2. The temperature for synthesis of the beryl crystal must be controlled precisely.
3. Significant amounts of flux must be used.
4. It is difficult to prevent feather inclusion from occuring.
5. The rate of crystal growth is slow.
Accordingly, it is desirable to provide a more economical process for preparing beryl crystals than the foregoing flux process. One such improvement is the use of a F.Z furnace in a zone floating method described by Akihiko Kochi in U.S. Pat. No. 4,218,282 which issued on Aug. 19, 1980 and assigned to the same assignee. In this process single crystals of chrysoberyl and beryl are prepared from feed rods formed of a desired composition wherein the feed rods are heated at one focus of a total ellipsoid mirror by a lamp positioned at the other focus of the ellipsoid mirror. The feed rod is held from above and below by axes rotating in opposite directions with the feed rod supported in a sealed, transparent quartz tube so that the atmosphere surrounding the feed rod can be controlled. A melt zone is formed in the feed rod and displaced along the rod by moving the rotation axis vertically. While this improvement has been satisfactory, it is desirable to improve further the synthesis of beryl crystals.
In any improved process it is desirable to have the following characteristics.
1. Avoid use of a platinum crucible.
2. Reduced the amounts of flux used.
3. Control feather inclusion by a controlled parameter not present in the conventional flux process.
4. A rate of crystal growth relatively high compared to the flux process.
5. Control direction of crystal growth to increase efficiency of production.